Initial Situation

We installed WordPress with all its dependencies on Arch Linux / Manjaro. Now we want to Install Plugins.

Problem

On clicking the Install Button in the Admin menu a window pops up with the following Message:

Failed to connect to FTP Server

To perform the requested action, WordPress needs to access your web server. 
Please enter your FTP credentials to proceed. If you do not remember your 
credentials, you should contact your web host.

Solution

Like suggested on StackOverflow it is enough to add a single line of Code the File /wp-config.php in our WordPress Directory:

define('FS_METHOD', 'direct');